Education and Child Development Minister Jennifer Rankine said 15 of those cases required investigation by a departmental unit.

Of those, 10 investigations are ongoing, one allegation was substantiated and another was disproved.

None of the cases involved Families SA staff.

Ms Rankine said she was advised that only "a very small proportion" of allegations are substantiated.

"On average, in about 25 per cent of all cases the alleged perpetrator is another child," Ms Rankine said.

UniSA child protection expert Dr Elspeth McInnes said a "chronic" shortage of social workers to check on children in care could be raising their risk of suffering abuse or not feeling confident enough to report it.

An audit by the Guardian's office of 174 children in care found 45 (26 per cent) did not have regular contact with the same social worker and 34 (21 per cent) met with their social worker less often than the expected monthly contact.

A further 11 children (6 per cent) were not assigned a social worker and in 13 cases social workers were found to have limited knowledge of a child's circumstances.

Overall, 151 children (87 per cent) were "confidently" considered safe.

Dr McInnes said children's safety was greatly dependent on the rigour of background checks on carers.

"Where you have people contracted to look after vulnerable children that will be a kind of profession targeted by people who prey on children," she said.

Ms Rankine said her government had overhauled child protection with a "greater focus on early intervention and prevention".

Opposition child development spokesman David Pisoni said it was "very, very difficult" to get information from the government on children in state care.

He questioned what support was available to children who made allegations of sexual abuse.